hesitation

internalcombust

internalcombust

New member
So I have been having some hesitation in the wagon. Its an 03 wrx wagon stage 2 with 55000 miles. At part throttle from 2000rpms to about 3500 or so it doesn't pull smoothly. At wide open it pulls fine, but part throttle it hesitates slightly. I had this problem before stage 2 and I did a full 60k service. I was hoping new plugs and a fuel filter would take care of it. I even tried some fuel injector cleaner with no results. If I reset the ecu it runs smoothly for a few trips then back to stumblesville. Its not bad but bad enough so I can notice it. The wife can't feel it when we drive so it is subtle. I think it is the front 02 sensor throwing some bad readings, but not bad enough to throw a code. How long do the 02 sensors generally hold up on a wrx? Has anyone had similar issues? Would a bosch 02 sensor be up to my stage 2 levels or should I go with stock subie replacement?

I haven't found any obvious vacuum leaks, and everything seems to fine under the hood. I really feel it is sensor related. Help me out if you can.

 
No code eh? That's gonna be tough. Does your accessport keep CEL's from coming on when they should? Is that how it's set? Are you catless? I can't remember. What's your up-pipe situation?

 
Sounds similar to the issue with the RS which was the front O2. They seam to go pretty common amongst subies. I would go with OEM for senors like that. Might even be worth haveing Patriot or Evergreen putting it on the diag to make sure of the issue (make sure you get someone who knows what they are doing the first time). That way you are not throwing a ton of money at the wrong problem.

 
The RS was never throwing an O2 code; Fuel trim and misfire. But the hesitation had been going on a while before the CELs started. Subtle at first like internal is taking about.

So without any codes the diag wont pick up a bad sensor even if it's just starting to go bad?

 
Not in a 1 hour diag >
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Maybe if you compare freeze frame data from a car that runs perfect to Internals, maybe, just maybe, if you look at the right sensor info at the right RPM and compare, you'd get lucky. But that ain't no 1 hour diag. that's a "drop it off, we'll fix it and tell you what you owe when it's done" Could be costly.

 
The RS was never throwing an O2 code; Fuel trim and misfire. But the hesitation had been going on a while before the CELs started. Subtle at first like internal is taking about.

So without any codes the diag wont pick up a bad sensor even if it's just starting to go bad?
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But it was throwing a code.
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I have absolutely no idea how this "diag" tool works, so if a car is not running right, but does not have a CEL the diag will not be able to pick anything up? Easily anyway?

 
Has this hesitation since you've gone to stage two only happened when its really hot outside? If so, my guess is the air is too hot and your knocking and the ecu is pulling some timing. Of course I dont know what the cobb map looks like. Because heat is the enemy, the map that I use on the street, normally with an intake air temp(IAT) of 60 or lower I will run 18 lbs of boost, but that tapers down to about 15.5 when the IAT is over 90 (as it generally has been lately, especially once everything gets heat soaked...) But, when its really hot, sometimes I wont get smooth power mainly because of timing being pulled.

Also, I'd be interested to see what the target boost levels and the Wastegate Duty Cycles are, because if you are are hitting more than the target, I'm wondering if its opening and closing the wastegate to limit boost as you are hitting targets too quick. Gabe would probably know more of that item than I would.

 
you know... i've been having the same thing, but i just atributied it to bad engine mounts or a failing sensor. but now that you mention it. it only really did it on REALLY hot days, lewiston for example.... maybe i should run a higher octaine, or figure out how to get colder air into the intake

 
you know... i've been having the same thing, but i just atributied it to bad engine mounts or a failing sensor. but now that you mention it. it only really did it on REALLY hot days, lewiston for example.... maybe i should run a higher octaine, or figure out how to get colder air into the intake
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Well.. once everything is heatsoaked.. it takes a little while to cool down, (a long while if you are not cruising down the road and your car is off) and its really hard because we just sit there for a god aweful amount of time just idling, it really doesn't do much for your car...

 
Also, I'd be interested to see what the target boost levels and the Wastegate Duty Cycles are, because if you are are hitting more than the target, I'm wondering if its opening and closing the wastegate to limit boost as you are hitting targets too quick. Gabe would probably know more of that item than I would.
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I concur. After awhile of you driving the snot out of the car it probably becomes more aggressive with WGDCs and the end result is it winds up searching for your boost targets at partial throttle. If you are really motivated try reseting the ECU and never opening it up more than 50% throttle and see if the hesitation doesn't return.
If the front O2 sensor were off you would most likely see immediate hesitation at light throttle low/mid rpms followed by pretty bad bogging 3500 - 4000 rpms after a couple of days up to a week.

 
Thanks for the input guys, I'm leaning towards the front 02 sensor. It happens all the time worse before the engine is off the initial enrichened circuit. Heat is not the issue. It was happenig before stage 2 upgrades. Feels like an 02 sensor.

 
that sensor could be toasted after the last owner feeding it nitrous i'm sure that's not to good for an o2 sensor >
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oh and buy a friggin passenger side window switch for f- sakes...........or you could spend more money on some hp you dont use...........

 
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